Transcript PowerPoint to accompany

Immunity to Infection
•
•
•
•
Obviously protecting the host from infection is the main
goal for the immune system
The immune system as an integrated defense mechanism.
The first thing to remember is that most microorganisms
arriving at the external surfaces of the body fail to establish
a colony. Just as in military strategy, the hardest thing for
an invader to do is to establish a beachhead.
So one cardinal property which distinguishes
microorganisms capable of colonising hosts from the much
larger number which can not is their ability to overcome
the physical and physiological barriers which protect the
surfaces of the body.
Immunity to Infection
•
•
•
•
Even then the majority of colonising organisms do not
penetrate the body's surface
Indeed the presence of these harmless commensal bacteria
makes a significant contribution to keeping out
undesirables.
Pathogens, then are that rather select group which can both
colonise and invade the body
There are a very small number of exceptions to this (almost
all gut bacteria) which can cause disease by secreting toxins
which damage the host without the organisms themselves
penetrating the body surface.
Immunity
• resistance to particular pathogens or to their toxins or
metabolic by-products
• based on the ability to distinguish “self” from “non-self”
• antigens elicit immune responses
Antigens
• proteins
• polysaccharides
• glycoproteins
• glycolipids
• most effective are large and complex
• haptens are small molecules that are not
antigenic by themselves
4
Body Defenses Against Infection
• Pathogen
• Disease causing agent
• Bacteria, Viruses, Parasites, Fungi
• innate defenses
• general defenses
• protects against many
pathogens
• adaptive defenses
• immunity
• more specific
• carried out by lymphocytes
Innate Defenses
•
•
•
Early Immune responses (4-96 hrs)
The immediate defenses are available
instantly or within an hour or so of
invasion
The recognition of foreign antigens
triggers the adaptive immune response
by the de novo synthesis of cytokines etc.
Innate Defenses
• Species Resistance
• resistance to certain
diseases to which other
species are susceptible
• Mechanical Barriers
• skin
• mucous membranes
• Chemical Barriers
• enzymes in various body fluids such
as Amylase
• pH extremes in stomach
• Fever
• inhibits microbial
growth
• increases phagocytic
activity
Innate Defenses
Inflammation
•
Acute inflammation is a short-term process, usually
appearing in a few minutes or hours
•
Ceasing once the injurious stimulus has been removed
•
It is characterized by five cardinal signs:
rubor (redness),
calor (increased heat),
tumor (swelling),
dolor (pain)
functio laesa (loss of function).
Innate Defenses
Inflammation
• tissue response to injury
• helps prevent spread of pathogen
• promotes healing
• blood vessels dilate
• capillaries become leaky
• white blood cells attracted to area
• clot forms
• fibroblasts arrive
• phagocytes are active
'Natural' antibody
•
Even when an organism is encountered for the
first time there may be some IgM antibody
which may bind
to its' surface structures
•
This is called 'natural' antibody
•
low affinity
•
It should be recognised that even very low
affinity reactions with IgM can trigers the
reactions
Innate Defenses
Phagocytosis
Destruction of foreign particles
• Neutrophils
• Monocytes
• Macrophages
Innate Defenses
Phagocytosis
•
•
•
•
•
•
Macrophages: resident in almost all tissues particularly
in large numbers in mucosal tissues
Neutrophils are present in the blood in very large
numbers
Neutrophils can be rapidly recruited to any site which
innitiate inflamatory reactions and/or activates
complement
Both types of phagocyte possess receptors which enable
them to bind and phagocytose microbial organisms
These receptors recognise molecules such as
carbohydrate structures which are not present on host
cells
Once organisms are engulfed, they are subject to a
battery of chemical and enzymatic attacks which in
many cases destroys them.
Innate Defenses
Interferon
•
Interferon alpha/beta are produced by a variety of cells
(Leukocytes & fibroblasts) in response to viral infection
•
They have an important role in limiting viral infection
in the early phase (before specific immunity is
available)
•
They do this both directly and indirectly.
1.
They act on a wide variety of cell types to induce the
synthesis of
a series of proteins which interfere with viral replication both by
degrading RNA and by inhibiting
2.
They also potently activate NK cells.
protein synthesis.
Innate Defenses
Natural Killer Cells (NK Ceels)
•
•
•
•
•
•
A type of lymphocyte
Lyses of viral-infects cells and cancer cells
These lymphocytes lack some antigen specific
receptors of T and B cells.
They are part of the innate immune system
They play an important role in viral
infections.
They are activated by the cytokines IL12 and
IFN alpha/beta.
Innate Defenses
Complement